This invention pertains to an improved grid plate assembly used for providing uniform upward flow distribution in liquid phase ebullated bed catalytic reactors. It pertains particularly to such grid plate assembly which utilizes multiple flow distributor tubes covered at their upper ends by caps which preferably have tapered side walls.
It is known that ebullated bed catalytic reactors operating at elevated temperature and pressure conditions are sometimes subject to flow maldistribution in the catalyst bed. Such flow maldistribution is usually due to abnormal operating conditions such as plugging of openings in the grid plate by coke, or to excessive coke deposits on the catalyst particles in the bed. If such plugging of openings in the grid plate occurs, non-uniform flow distribution and bed ebullation occurs, which is very undesirable. Also, if slumping of the ebullated catalyst bed ever occurs due to any interruption of upward liquid flow from the recycle pump or due to other severe operational upset conditions, difficulty is sometimes encountered with completely re-ebullating the entire catalyst bed.
The use in such ebullated bed catalytic reactors of conventional cylindrical riser tubes covered by cylindrical-shaped bubble caps is disclosed by U.S. Pat. No. 3,197,286 to Farkas et al; U.S. Pat. No. 3,197,288 to Johanson, and U.S. Pat. No. 3,475,134 to Weber et al. However, it has been found that fine catalyst particles together with heavy hydrocarbon liquid fractions under conditions of high temperature can become partially coked and plug these conventional riser conduits. Also such coked catalyst particles can become packed into the spaces between conventional cylindrical-shaped caps having parallel sides, thereby making the uniform re-ebullation of a slumped catalyst bed much more difficult to accomplish. Thus, improvements in ebullated bed reactor flow distribution have been sought. An improved grid plate configuration has been developed which effectively redistributes the gas and liquid flows above the grid plate whenever flow maldistribution problems exist below the grid, facilitates re-ebullation of a slumped catalyst bed, and also provides for monitoring the temperature of the bed above the grid plate to determine that uniform ebullation of the catalyst bed has been established.